As enraged Muslims take to the streets to protest cartoons depicting the prophet Muhammad, few seem to be aware that representations of Islam's last messenger have existed throughout history without causing alarm."There is nothing in the Quran that forbids imagery the way it is condemned in the Hebrew Bible," said John L. Esposito, university professor of religion and international studies at Georgetown University.Although rare in the 1,400 years of Islamic art, visual representations of Muhammad were acceptable in certain periods. Today, his likenesses grace collections around the world, at New York's Metropolitan Museum of Art, the Edinburgh University Library, the British Museum and the Bibliotheque Nationale de France in Paris."To say that Islam is anti-imagery is to have a very limited understanding of the religion," said Linda Komaroff, curator of Islamic art at the Los Angeles County Museum of Art. "Islam isn't just one flavor or one interpretation"The museum has an unusual depiction of him -- a verbal portrait. Called a hilyeler, meaning adornment, the verbal portrait was common during the Ottoman period and often could be found hanging in Muslim homes."They were the equivalent of the paintings of Jesus Christ or Virgin Mary one finds in Christian homes today," Komaroff said.The hilyeler in Los Angeles is a description of Muhammad by his son-in-law, Ali. It has been translated as follows: "He was not too tall or too short. He was medium-size. His hair was not short and curly, nor was it lank, but in between. His face was not narrow, nor was it fully round, but there was a roundness to it. ... Between his shoulders was the seal of prophecy, the sign that he was the last of the prophets."Esposito said the current belief by many Muslims that images of the prophet are sacrilegious probably stems from the Quran's strong denunciation of idolatry. "Worshiping an idol is the greatest sin in Islam," he said. "There is great emphasis in the Quran on not associating anything with God."One of the most repeated stories about Muhammad in Islamic history narrates an incident in which he entered the Holy Kaaba, a Muslim shrine, and destroyed all the idols standing inside.But Ingrid Mattson, professor of Islamic Studies at Hartford Seminary, said Muslims aren't upset just because the Danish cartoons disregard their religious beliefs. "These are racist depictions," she said. "They are along the lines of anti-Semitic depictions once seen in Europe. They are deliberately offensive and aimed at a minority which is already feeling marginalized."Other Muslim activists said the images misrepresented the prophet by showing him as a terrorist, whereas he was a peace-loving man.The modern-day blanket prohibition of portraying Islam's sixth century messenger can probably be credited to the strict teachings of Wahabi Islam, said Jonathan Bloom, an Islamic art historian at Boston University. Wahabi is the Saudi Islamic sect founded in the 18th century that is the official ideology of Saudi Arabia and supposedly practiced by Osama bin Laden."There were definitely times, especially in Iran in the 14th century and during the Ottoman empire, when manuscripts contained illustrations of him," Bloom said.Probably the most well-known illustration of the prophet is contained in the "Book of the Assumption of Muhammad," dated around 1425 and thought to be painted in Herat, Afghanistan. Called the meraj-nama, it shows Muhammad mounted on a horse and being guided on a tour of Paradise. The original can be found at the National Library in Paris.Renowned Western artists such as Salvador Dali, Auguste Rodin, William Blake and Gustav Dore have made paintings of Muhammad in their illustrations of the Inferno chapter of Dante's trilogy "The Divine Comedy."Muslim activists in the United States say examining the violent response to the Danish cartoons in isolation is a mistake."None of this can be explained as a response to one offensive cartoon," said Rabiah Ahmed, spokeswoman for the Council on American-Islamic Relations in Washington. "In the last few years, rhetoric of Western politicians and the war on terror have both fed into suspicions of Muslims that the West harbors hostility toward them and mocks their values. These cartoons added to the insult."Ahmed said previous disrespectful representations of the prophet did not provoke such a response, which is why attributing Muslim outrage solely to the Danish cartoon would be erroneous.In 2001, the television cartoon "South Park" aired an episode in which Muhammad teams up for superhero action and, a year later, the French publication Charlie Hebdo ran a cartoon showing the prophet drinking and smoking.A comic book titled "Mohammed's Believe It or Else!" contains hundreds of satirical cartoons. The book's Web site says it is being translated into six languages, including Arabic and Dutch.Although each of these depictions provoked anger from Muslims -- the comic's Web site claims to have received 14,000 death threats -- none of them culminated in a global protest.In the past century, the prohibition against showing Muhammad's face has hardened due to teachings of conservative Muslim leaders."In contemporary times, prophet Muhammad has become the most visible symbol of integrity of Islam," said John Voll, author of "Islam, Continuity, and Change in the Modern World." "Muslims have become extremely sensitive to any attack on the prophet's person."This is particularly so of the Sunni sect of Islam, in which imagery is frowned upon. Shiite Muslims indulge heavily in visual representations, and in Iran depictions of the prophet's son-in-law are common.Voll believes that had the cartoons attacked any Islamic figure other than Muhammad, the response might have been different."I don't think the reaction would have been this strong at all," he said. "Even in 'The Satanic Verses,' Muslims were upset at the defaming of Muhammad, and few seemed bothered that Muhammad's companions were also defamed in the book."The problem with the Danish cartoon seems to be that it insults Islam's most revered figure at a time when Muslims are particularly sensitive to Western perceptions."Muslims love the prophet Muhammad," said Mattson. "An attack on him is perceived as an attack on Islam."